Method for manufacturing filaments from an optically anisotropic spinning solution and air gap spinning device

ABSTRACT

The invention pertains to a method for manufacturing filaments from an optically anisotropic spinning solution in which the spinning solution is extruded through a spinneret including a spinning field with a plurality of spinning orifices into a coagulation bath through a slot or diaphragm, the edges thereof being formed by plates with upper and lower sides. The upper sides of the plates are defined as the sides having the shortest distance to the spinning field, wherein the line through the center of the spinning field and perpendicular to the upper sides is located a distance (d) from a parallel line through the center of the slot or diaphragm. The projection of the slot or diaphragm has about the same size and shape as the projection of the spinning field. The plane of the upper side of one plate has a shorter distance to the center of the spinning field than the plane of the upper side of the other plate, and the line has a smaller distance to the edge of plate than to edge of plate. Furthermore, the invention pertains to an air gap spinning device for performing the method.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is the U.S. National stage application ofInternational Application No. PCT/EP03/00471, filed on Jan. 18, 2003.

BACKGROUND OF THE INVENTION

1. Field of Invention

The invention pertains to a method for manufacturing filaments from anoptically anisotropic spinning solution in which the spinning solutionis extruded through a spinneret comprising a spinning field with aplurality of spinning orifices, into a coagulation bath through a slotor diaphragm, the edges thereof being formed by plates with upper andlower sides, the upper sides of the plates being defined as the sideshaving the shortest distance to the spinning field, and to an air gapspinning device for performing said method.

2. Description of Related Art

Such a method is known from European Patent No. 0,904,431, wherein ithas been disclosed that the motion of the coagulant surface can bereduced when the edges of adjacent openings are at different heights(“on different levels”). In the examples of said patent specification,filaments of good strength are made. This method, however, suffers fromthe disadvantage that the coagulation bath during the spinning procedureis still in continuous movement, which is particularly troublesome whenapplied on a larger scale. Such movement has a disadvantageous effect onthe filaments formed, since the filaments in the coagulation bath willstick together, rendering the end product unsuitable for use in theenvisaged high-grade applications (e.g., woven fabrics or compositereinforcement).

When very small air gaps are employed (say, smaller than 4 mm), there isa risk of the coagulant, which will always display some motion under theinfluence of the filament bundle (vibrations, small waves, etc.), makingcontact with the spinneret plate. When this happens, the process may bedisturbed to such a degree, that it will be required to be stopped.Hence, if very small air gaps are to be used, it is of the essence tohave the calmest possible coagulation bath surface. It was found thatthe extent to which the coagulation bath surface is in motion is highlydependent on the geometry of the coagulation bath's bottom.Particularly, when use is made of more than two spinning fields and acorresponding number of discharge openings in the bottom of thecoagulation bath, the extent to which there is motion at the coagulantsurface can be reduced substantially by introducing the geometry of thepresent invention. A very simple and effective embodiment that providesa substantial improvement of the known method is the one of the presentinvention.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a process enabling thehigh-speed spinning (>300 m/min) of a plurality of filaments having goodto very good physical properties, the process conditions being such thatcommercial production is possible without having disturbing effects ofthe coagulation bath surface. This object is attained by adapting theprocess of the state of the art as indicated above in such a manner thatthe positions of the spinning field and the slot or diaphragm are suchthat a line through the center of the spinning field and perpendicularto the upper sides of the plates is put at a distance (d) to a parallelline through the center of the slot or diaphragm, the projection ofwhich has about the same size and shape as the projection of thespinning field, and wherein the plane of the upper side of one plate hasa shorter distance to the center of the spinning field than the plane ofthe upper side of the other plate, and the line through the center ofthe spinning field has a smaller distance to the edge of the plate withthe upper side having the largest distance to the center of the spinningfield than to edge of the other plate.

The edges of the slot or diaphragm are formed by at least two plates,the upper side of one plate having a shorter distance to the spinningfield than the upper side of the other plate. The line through thecenter of the spinning field and perpendicular to the upper sides of theplates has a smaller distance to the edge of the plate with the upperside having the largest distance to the spinning field, than to edge ofthe other plate. The distance of the upper side of a plate to thespinning field can be defined as the shortest distance of the center ofthe spinning field to the plane of the upper side of the plate.

Surprisingly, it was found that this process makes it possible tomanufacture filaments having good physical properties at a small pitch(and hence a large number of filaments per unit of area) at acomparatively high acid concentration in the coagulation bath, resultingin an economical process with a small waste stream. As can be seen fromthe example, the number of stickings occurring during the process (fromfilaments making contact before there has been sufficient coagulation ofthe outer shell) is low. No substantial motion occurred in thecoagulation bath. A possible explanation of this phenomenon is givenbelow.

At the edges of the discharge openings, the liquid, which is entrainedby the outgoing filament bundle is stopped or scraped off. Because ofinertia, the liquid retains (part of) its speed and flows parallel tothe bottom in the direction of the adjacent discharge opening. However,coagulant flow also approaches from the direction of this adjacentdischarge opening, resulting in the collision of streams flowing inopposite directions. The liquid is pushed up as a result, and thecoagulation bath surface rises above this stagnation point. Obviously,the damming up of the coagulant constitutes a significant restrictionwhen selecting the air gap; after all, the coagulant has to be preventedfrom making contact with the spinneret plate.

When the aforementioned streams come together at different levels, thedisclosed damming up does not arise. On the contrary, because the speedof one of the streams (i.e., the one flowing from the lowest edge)already has a component going in the direction of the liquid surface,there is extinction and the liquid surface remains calm.

When the coagulation bath has a depth of more than 10 mm and less than20 mm (preferably less than 15 mm), on the one hand the filamentsencounter only slight resistance in the bath and the use of coagulant islow, and on the other hand the residence time in the coagulation bath islong enough to achieve the required coagulation.

The process according to the invention makes it possible to use acomparatively compact spinning apparatus or to equip existing spinningapparatus with spinneret plates with a higher number of spinningorifices. For instance, the production of 1000 to 3000 filaments perspinning position is possible.

The favorable results are probably attributable to the low resistanceexperienced by the coagulant as it flows to the core of the filamentbundle (alternatively, this may be referred to as high filament bundlepermeability). The resistance depends on the route to be traveled, i.e.,half of the width of the filament bundle, and the space between thevarious filaments (the pitch).

Preferably, the spinning orifices are grouped in more than one spinningfield. The separate sections can then be positioned vis-à-vis oneanother such as to ensure the least possible hindrance of thecoagulant's approaching flow and the fullest possible avoidance ofdisturbing the coagulation bath.

Also, the separate spinning fields preferably are positioned such thatthe maximum space between the outermost filaments is relatively small atthe moment of extrusion from the spinning orifices of the differentspinning fields, so that the convergence to, say, a guide, may be low.

One highly effective way of positioning the spinning fields takes theform of the spinning fields being distributed equidistantly over acircle, with the longitudinal direction of each of the spinning fieldscoinciding with a radius. Such positioning hinders the approaching flowof the coagulant hardly (if at all) and gives a low convergence for eachof the filament bundles. The spinning fields may have any desirableshape, but in many instances rectangular spinning fields are preferred.

To further reduce convergence in the filament bundle or filament bundlesit is preferred to provide the bottom of the coagulation bath perspinning field with an opening, the projection of which preferably has asimilar shape and is somewhat narrower in width than the projection ofthe spinning field. Furthermore, if the opening has a somewhat greaterlength than the spinning field, it facilitates the in-spinning process.In that case, neither the length nor the width of the opening in thebottom of the coagulation bath will give rise to substantial filamentbundle convergence, and the filaments are prevented from being pressedtogether or suffering damage from scraping along the edge of the slot ordiaphragm. In general the difference of the length and the width withregard to the spinning field should be moderate. Such difference ispreferably not more than 60% of the length and not more than 100% of thewidth of the spinning field, more preferably not more than 35% and 55%for the length and the width, respectively.

The physical properties of the filaments obtained by the processaccording to the invention can be enhanced still further by selecting arange for the distance traveled by the threadlike extrudates through thegaseous inert medium (the air gap) of more than 0.5 mm and less than 16mm.

Within the framework of the invention the term pitch is used to indicatethe average distance between the spinning orifice centers of adjacentspinning orifices.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further illustrated below with reference to anexample and figures, without being limited by this example.

FIG. 1 shows a bottom view of a spinneret according to the inventionprovided with eight rectangular spinning fields.

FIG. 2 shows a cross sectional view of a spinning device according tothe invention.

FIG. 3 shows a detail of the diaphragm of the spinning device of FIG. 2.

FIG. 4-6 show the effect on the occurrence of impoundments in acoagulation bath according to the invention and in reference baths notaccording to the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In FIG. 1, a spinneret 1 with eight rectangular spinning fields 2 isshown. Each spinning field 2 contains a plurality of spinning orifices 3(only depicted in one of the spinning fields).

In FIG. 2, a device according to the invention is shown to which themethod of the invention can be explained. The optically anisotropicspinning solution is extruded through a spinneret 1 comprising spinningfields 2 with a plurality of spinning orifices 3, into a coagulationbath 4 through a slot or diaphragm 5, edges 6 a,6 b thereof being formedby plates 7 a,7 b with upper sides 8 a,8 b and lower sides 9 a,9 b, theupper sides 8 a,8 b of the plates 7 a,7 b being defined as the sideshaving the shortest distance to the spinning field 2. A line 10 throughthe center 13 of the spinning field 2 and perpendicular to the uppersides 8 a,8 b is put at a distance d to a parallel line 11 through thecenter 14 of the slot or diaphragm 5. The center 14 is defined as thecenter of the area that is between and limited by the edges 6 a and 6 band the line 15 a being the line between the upper corners of edges 6 aand 6 b, and line 15 b being the line between the lower corners of edges6 a and 6 b, which area is the slot or diaphragm 5. In FIG. 3, the crosssection of this area and the center 14 are depicted.

The distance of a plate 7 a,7 b to the spinning field 2 is defined asthe shortest distance of the plane of the upper side of the plates 7 a,7b and a perpendicular plane through the center 13 of the spinning field2. In FIG. 4, the distance “a” between perpendicular plane through thecenter 13 of a convex-shaped spinning field 2 and the upper side 8 b ofplate 7 b is depicted.

In another embodiment (not shown), one of the plates is thicker than theother plate. When the lower sides of these plates are brought at thesame or about the same height, the upper sides of the plates will havedifferent distances to center 13 of the spinning field 2. In allembodiments, each of the spinning fields 2 is in combination with a slotor diaphragm 5. One slot or diaphragm 5 cannot be in contact (throughthe spinning fibers) with more than one spinning field 2.

The thickness of each of the plates 7 a,7 b is preferably independentlychosen to be between 0.5 and 5 mm.

It is preferred that the air gap spinning device of the invention has ashorter distance of plate 7 b to the spinning field 2 than of the otherplate 7 a to said spinning field 2, and that line 10 has a smallerdistance to edge 6 a of plate 7 a than to edge 6 b of the other plate 7b. The distance d thereby is preferably 0.4 to 50 mm, more preferably 1to 2 mm.

It was found to be particularly useful to have plates 7 a,7 b with athickness that is about the same as the distance d between the line 10and the line 11.

Particularly good results are obtained when (the projection of) the slotor diaphragm 5 has about the same size and shape as that of the spinningfield 2. In practice, the slot or diaphragm 5 has the same shape, but ispreferably slightly smaller than the spinning field 2. When,furthermore, the slot or diaphragm 5 is slightly longer than thespinning field, in spinning is facilitated. The spinning device ispreferably closed with a covering plate just above the slot or diaphragm5 (not shown).

EXAMPLE

In an analogous manner to the procedure described in Example 6 of U.S.Pat. No. 4,308,374, poly(para-phenylene terephthalamide) was preparedusing a mixture of N-methyl pyrrolidone and calcium chloride. Afterneutralization, washing and drying, a polymer having an inherentviscosity of 5.4 was obtained.

The polymer was dissolved in sulfuric acid of 99.8% concentration in themanner described in Example 3 of U.S. Pat. No. 4,320,081. The thusprepared spinning solution had a polymer concentration of 19.4%.

The spinning solution was spun using different spinneret/diaphragmembodiments (see FIGS. 4-6).

A circular spinneret 1 according to the spinneret disclosed in EuropeanPat. No. 0,904,431, having an outer diameter of 90 mm was provided witheight rectangular spinning fields 2 (2.65 mm width and 18.4 mm length)each having 250 spinning orifices 3, and being distributed equidistantlyover the spinneret 1. The spinning orifices 3 had a diameter of 65 μmand a distance of one to the other (pitch) of 0.5 mm (the ratio of thepitch to the width of the spinning field 2 thus was 0.5/2.65=0.19).

The spinning solution was spun through an air gap of 6 mm length into acoagulation bath. The coagulant was made up of water having a sulfuricacid concentration of 2% and a temperature of 13° C. The spinning speedwas 300 m/min and the draw ratio was 6.8 to a total fiber bundle of 3360dtex. The physical properties were determined in accordance with ASTMD885.

At 10 mm below the surface of the coagulation bath there were providedeight diaphragms (rectangular 1.26 mm×24 mm) each of which can bepositioned slightly shifted beneath a spinning field. The diaphragmplates 7 a,7 b could be shifted both at the same time in the samedirection perpendicular to the filaments, by which the positioning waspossible of the diaphragms 5 with respect to the spinning fields 2. Theshift distance could be read from a grade mark. By this method, line 10through the center 13 of the spinning field 2 and perpendicular to uppersides 8 a,8 b of the plates 7 a,7 b could set at a distance d to aparallel line 11 through the center 14 of the diaphragm 5, varying from−10 to +10 mm (including 0 mm when lines 10 and 11 coincide with eachother).

When d was set at 0 mm, spinning was practically impossible because ofthe severe coagulation bath movements with impoundments of the bath ashigh as 5 mm. This is shown in FIG. 4, a comparative example.

A similar occurrence of movements resulting in impoundments up to 4 mmheight is shown in FIG. 5 wherein the spinning fields 2 are shifted withdistance d minus 1.5 mm in the direction of plates 7 b with the uppersides 8 b having the shortest distance to the centers 13 of the spinningfields with regard to the upper sides 8 a, a comparative example.Spinning was very difficult in this embodiment and it was necessary tolengthen the air gap to unacceptable dimensions.

Furthermore, a substantial increase of the degree of sticking of thefilaments was found (up to 25% of the filaments were subject tosticking).

In FIG. 6, a situation is shown wherein the spinning fields 2 areshifted with distance d plus 1.5 mm in the direction of plates 7 a withthe upper sides 8 a having the largest distance to the centers 13 of thespinning fields with regard to the upper sides 8 b. No disturbingmovements of the coagulation bath occurred and spinning could easily beperformed. Yarn was made with this embodiment having a bundle lineardensity of 3420 dtex, yarn tenacity 2225 mN/tex and <1% degree ofsticking.

It was found that optimum results were obtained for 0.5 mm<d<2 mm.

1. A method for manufacturing filaments from an optically anisotropicspinning solution comprising extruding the spinning solution through aspinneret comprising a spinning field with a plurality of spinningorifices into a coagulation bath through a slot or diaphragm, the edgesof the slot or diaphragm being formed by plates with upper sides andlower sides, the upper side of each plate being defined as the sidehaving the shortest distance to the spinning field, wherein a linethrough the center of the spinning field and perpendicular to the uppersides is located at a distance (d) from a parallel line through thecenter of the slot or diaphragm, wherein the slot or diaphragm hassubstantially the same size and shape as the spinning field, and whereinthe plane of the upper side of one of the plates has a shorter distanceto the center of the spinning field than the plane of the upper side ofthe other of the plates, and the line through the center of the spinningfield has a smaller distance to the edge of one of the plates than tothe edge of the other of the plates, and wherein the slot or diaphragmis positioned at the bottom of the coagulation bath.
 2. An air gapspinning device comprising a spinneret comprising a spinning field witha plurality of spinning orifices, and a slot or diaphragm with edgesformed by plates with upper sides and lower sides, the upper side ofeach plate being defined as the side having the shortest distance to thespinning field, wherein a line through a center of the spinning fieldand perpendicular to the upper sides has a distance (d) from a parallelline through the center of the slot or diaphragm, wherein the slot ordiaphragm has substantially the same size and shape as the spinningfield, and wherein the plane of the upper side of one of the plates hasthe shorter distance to the center of the spinning field than the planeof an upper side of the other of the plates, and the line through thecenter of the spinning field has a smaller distance to the edge of theplate of which the upper side has the longest distance to the center ofthe spinning field than to the edge of the other of the plates, andwherein the slot or diaphragm is positioned at the bottom of thecoagulation bath.
 3. The air gap spinning device of claim 2, wherein thethickness of each of the plates is independently about 0.5 to 5 mm. 4.The air gap spinning device of claim 2, wherein the distance (d) betweenthe line through the center of the spinning field and the parallel linethrough the center of the slot or diaphragm is about 0.4 to 50 mm. 5.The air gap spinning device of claim 2, wherein the distance (d) betweenthe line through the center of the spinning field and the parallel linethrough the center of the slot or diaphragm is about 1 to 2 mm.
 6. Theair gap spinning device of claim 2, wherein the thickness of each of theplates is about the same as the distance(d) between the line through thecenter of the spinning field and the parallel line through the center ofthe slot or diaphragm.
 7. The air gap spinning device of claim 2,wherein both the spinning field and the slot or diaphragm have arectangular shape, and wherein the slot or diaphragm has a smaller widthand is longer than the spinning field.